Differential effect of aging on B-cell immune responses to cholera toxin in the inductive and effector sites of the mucosal immune system.

The age-associated primary immune response of B cells from the Peyer's patches (PP), the lamina propria (LP), the mesenteric lymph nodes (MLN), and the spleen of mice following oral immunization with cholera toxin (CTx) was investigated. The induction of immune responses was assessed in 4-, 11-, and 24-month-old, individual C57BL/6J male mice by determining the number and isotype of anti-CTx ELISPOT-forming cells (SFC) in the PP, LPL, MLN, and spleen and the titer and isotype of serum anti-CTx antibody. The data indicate a significant age-associated decline in immunoglobulin G (IgG) and IgA anti-CTx SFC in the LP B cells but only in IgA anti-CTx SFC in the PP. No decline was seen in the anti-CTx SFC response in the MLN and spleen. Peroral immunization of mice with CTx resulted in a serum anti-CTx antibody response which was predominantly of the IgG class in all three age groups of mice tested. There was no age-associated decline in anti-CTx IgM, IgG, or IgA titers in serum. Isoelectric focusing and affinity immunoblotting revealed several distinct new antibody clonotypes in the immune serum of old mice following oral immunization with CTx. The results indicate a loss of immune responsiveness to CTx following oral immunization in senescent PP and LP B cells. The MLN and spleen B-cell responses were found to be refractory to the loss of immune function with aging. These findings suggest a differential effect of aging in the inductive and effector sites of the mucosal immune system, and the loss of antigen-specific IgA responses at mucosal sites may have adverse effects on the host's defense against potential pathogens.